The automatic nervous system (ANS) regulates “involuntary” organs. The ANS includes the sympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system is affiliated with stress and the “fight or flight response” to emergencies. The parasympathetic nervous system is affiliated with relaxation and the “rest and digest response.” The ANS maintains normal internal function and works with the somatic nervous system. Autonomic balance reflects the relationship between parasympathetic and sympathetic activity. A change in autonomic balance is reflected in changes in heart rate, heart rhythm, contractility, remodeling, inflammation and blood pressure. Changes in autonomic balance can also be seen in other physiological changes, such as changes in abdominal pain, appetite, stamina, emotions, personality, muscle tone, sleep, and allergies, for example.
Neural stimulation therapy has been proposed for a variety of reasons. Reduced autonomic balance (increase in sympathetic and decrease in parasympathetic cardiac tone) during heart failure has been shown to be associated with left ventricular dysfunction and increased mortality. Research also indicates that increasing parasympathetic tone and reducing sympathetic tone may protect the myocardium from further remodeling and predisposition to fatal arrhythmias following myocardial infarction. Direct stimulation of the vagal parasympathetic fibers has been shown to reduce heart rate via the sympathetic nervous system. In addition, some research indicates that chronic stimulation of the vagus nerve may be of protective myocardial benefit following cardiac ischemic insult. Neural stimulation also has been proposed to alleviate pain and as a therapy for hypertension.
It can be difficult to anticipate the amount of energy needed for neural stimulation. For effective therapy, it may be necessary to stimulate neural targets intermittently or continuously. Also, high current levels may be effective for a larger area, or lower levels may be effective for a smaller area. A flexible power management system is needed to improve neural stimulation devices.